Plugin integration

I have recently purchased the Relevenssi plugin to improve the searchability of my schools website. I have been working with the plugin’s developer to integrate it into the Alora theme that we are using. The problem that I am running into is that our website utilizes multisite and in order to get the built-in wp search to use the Relevenssi plugin to search through all of the blog sites instead of just the blog the user is currently in, I need to modify the searchform to include a searchblogs parameter.

What I am wondering is, what file includes the search parameters? I tried modifying the searchform.php file, but from the way the search is responding, that is not where I need to make the change.

The plugin developer though it could possibly be in the header or sidebar files, but I was unable to locate it. Could someone point me in the right direction so I can get this working properly?